The present invention relates to a printed circuit board (hereafter referred to as PCB), in which a High frequency circuit, a reference signal generating circuit or the like formed on the PCB is shielded in order to prevent the radiant noise generated from the copper printed circuits carrying h.f. signals from adversely influencing the rest of the system.
The conventional shielded PCB is shown in FIG. 3. In FIG. 3, electric parts 1 are soldered to a PCB 2 at a predetermined point so that a noise generating circuit portion 3, such as a high frequency circuit and a reference signal generating circuit, is formed on PCB. In which, the noise is radiated from circuit elements, copper patterns or the like.
In such PCB, thin slots 4 are provided around the noise generating circuit portion 3 to receive pawls 5a of a shield case 5 made from metal. Thereafter, a shield case 6 is placed on the back of the PCB 2, and the shield cases 5 and 6 are connected by soldering or the like.
The conventional shield for the PCB covers the electric parts 1 of the noise generating circuit portion 3, so that the volume of the shield case becomes large. Therefore, it is difficult to provide high density PCB products using such conventional arrangements.
Further, air flow is interrupted or prevented by the shield cases 5 and 6, so that the heat generated from the electric parts 1 remains in the shield cases 5 and 6. Therefore, the temperature characteristic of the elements cause them to be adversely affected.
Furthermore, the manufacturing cost becomes large by the cost of the die of the shield cases, parts or the assembling.